The Pima County Wastewater Management Department (PCWWM), in Tucson, Arizona has been funded by the U.S. Environmental Protection Agency (EPA) to conduct the Arid West Water Quality Research Project (WQRP). The objective of the project is to improve the scientific base for regulation
of water quality, protection of species, habitats, and uses of watercourses, and designation of appropriate treated wastewater effluent controls in ephemeral and effluent-dependent watercourses of the arid and semi-arid western states. Effluent dependent ecosystems are streams that but for
the perennial flow from wastewater treatment plants, would otherwise be dry during some or all of the year. In some lowland desert areas, effluent dependent waters are the dominant form of perennial stream, thus providing important habitat for aquatic and terrestrial species.The following
statement will be explored throughout the paper: Concentrations of certain chemical constituents in the arid west, particularly hardness and alkalinity, are significantly higher than in most fresh water streams elsewhere around the country.As a measure of how chemical composition
and ionic strength may affect arid and semiarid west streams, the project team compared the water chemistries from 10 project sites (arid streams) to other fresh water systems elsewhere in the country using three methods. The first method compared western stream chemistries with standard WET
testing water chemistry. The second method compared the western stream chemistries to toxicity database water chemistries used in deriving aquatic life criteria for ammonia, cadmium, copper, and zinc. The third method compared the western stream chemistries with the water chemistries from
selected non-arid streams. In addition, the relative impact of wastewater treatment plant discharge on the arid versus non-arid streams was evaluated.

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Document Type: Research Article

Publication date: 2001-01-01

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